Could Obesity Change The Brain?

A fatty diet may trigger inflammation of the hypothalamus, deep inside the brain, and hinder weight loss.

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The standard advice for losing weight often comes up short for people who are obese.

If they switch to a healthful diet and exercise more, they might lose a bit. But the pounds have a way of creeping back on.

Now some provocative research suggests that a part of the problem might be that obesity could change the area of the brain that helps control appetite and body weight.

And those changes might start within a day of eating a high-fat meal, according to scientists who are trying to figure out why it's so hard to lose weight. They report seeing changes in the brain after just one day on a fatty diet.

"That was quite a shock," says Michael Schwartz, a professor and director of the Diabetes and Obesity Center of Excellence at the University of Washington. "This might reflect fundamental biological changes in how the brain works that help explain why it's so hard to keep weight off."

He fed rats and mice a high-fat diet, similar to what people in the United States typically eat, and found inflammation in the hypothalamus after just one day, well before the animals gained any weight. They were looking at the hypothalamus because it's the part of the brain that helps regulate body weight and hunger. Earlier studies in obese lab animals have found inflammation there.

Within a week, the animals' brains mounted a defense, activating cells in the brain that repair and protect damaged neurons. The inflammation subsided. But after about a month, the inflammation returned, and continued for eight months, when the researchers ended the study. The results were published in the Journal of Clinical Investigation earlier this week.

Yes, these are animal brains, and human brains might not respond the same way. But Schwartz's team did look at MRI scans done on the brains of 34 people, and found that the people who were obese had more of that repair activity in the hypothalamus than did people of normal weight.

Still, at this point these are just clues as to what might be going on in the brains of people who are obese, and Schwartz is the first to admit that. He's now studying rodents who are switched to a healthful diet after gaining weight, to see if their brains return to normal.

Should we non-rodents be worried? "I would be concerned about this," Schwartz told Shots. "If we can see these responses occurring rapidly with eating high-fat foods in excess, maybe we as humans should think that there are potential consequences for indiscriminate eating."

Not what you want to hear right after a big-eating holiday.

But that spike in inflammation after a pigout could also be a protective response, another scientist says. "My sense is that a lot of it is adaptive," says Rexford Ahima, an endocrinologist at the University of Pennsylvania Perelman School of Medicine. "It may be a good thing."

Ahima co-wrote a commentary on Schwartz's research. He thinks the brain's fast response to fatty food might prove to be normal, like the insulin spike that people get after a big meal. The important brain changes, Ahima speculates, might come when a lab rat has eaten enough to become obese and the brain inflammation is constant.

Whether that also applies to humans who indulge in occasional pigouts, but also overeat day after day, remains to be seen.